The information about the "duration" of the timer execution displayed in Service Center is computed based on the ossys_cyclic_job.is_running_since system table. The scheduler service is responsible for the maintenance of the coherence of this table (based on the timers that executes).

On the other hand, a timer request is simply a web service request executed by the Scheduler Servicer to your application (the web service is internaly generated by the outsystems platform).

From this information you can deduce two things:
1. If you restart IIS, the timer stops (as a timer is simply a web service request, this means a iisreset will definitely kill your timer execution).
2. If the information about the duration in the Service Center appears wrong even after an IISReset and a Scheduler Service restart, this means that somehow the information in the system table became inconsistent on the database (i.e. the scheduler service was not able to update the ossys_cyclic_job.is_running_since timer entry correctly). To correct it you can run the timer again (so that the scheduler service corrects it).

Your answers may all be correct but somethimes in Outystems none of those methods work to reset the timer. You really have to go to the database to the tables OSSYS_CYCLIC_JOB or OSSYS_CYCLIC_JOB_SHARED (depending on if its multi tenant or not http://www.outsystems.com/forums/discussion/14792/difference-between-system-tables-for-scheduler/) and kill the job erasing the field in "IS_Running_BY" collumn and placing a zero at the field in "NUMBER_OF_TRIES" Collum".

Be careful anyway this is not supported or recommended by Outsystems (since it's changing the database), but it works!! For me it was the only way...

For other nicer way to avoid to do this we have to wait for Outsystems to implement something like is suggested in the page https://www.outsystems.com/ideas/122/make-it-possible-to-abort-a-running-timer-through-service-center

let's say you have 100 records to process.
then we do 10 and call the timer again.
but the first action in the start will be "UseKillSwitch"-boolean, so we always can kill a timer when needed.
that boolean can be a database or a site-property ofcourse.